1. Field of the Invention
This invention relates generally to plasma deposition and etch equipment used in the fabrication of integrated circuits and, more specifically, to plasma-resistant coatings for use on internal chamber components of such equipment.
2. Description of the Prior Art
The manufacture of integrated circuits from conductive, semiconductive and dielectric materials has spanned a plethora of manufacturing equipment and processing techniques. The deposition of thin films, the application of photoresist mask patterns, and the selective etching of one or more layers, and the removal of residual mask patterns are essential steps in the manufacture of integrated circuits. A variety of techniques are currently used for deposition, etching, and photoresist removal. A typical process may involve the creation of a photoresist mask pattern, a subsequent etching of areas unprotected by the mask pattern, and the removal of the residual photoresist. There are two basic kinds of etches: wet and plasma.
Using a wet etch, a substrate is immersed in a chemical bath that attacks the substrate or the resist. While wet etches are conceptually straightforward, they are almost invariably isotropic. That is, a wet etch proceeds in all directions at the same rate. This leads to undesired lateral etching under the edges of the mask pattern. This undercutting effect limits the dimensional control that can be achieved with a wet etch. As features become smaller with each new generation of integrated circuits, the need to improve dimensional control increases. An additional disadvantage to wet etches is that they require the storage, handling, and disposal of toxic chemicals, such as hydrofluoric acid.
Plasma environments in a reactor chamber provide an alternative processing technology for deposition, etching, resist removal, and the like. A plasma is a nearly electrically neutral ionized gas. It contains a substantial density of free electrons and positively charged ions. To remain ionized, a gas must constantly receive energy to offset the recombination of charged particles which occurs most on the walls of the reactor chamber. Plasmas for anisotropic (single or down-direction) etching are typically generated by applying a radio-frequency (RF) electric field to a gas held at low pressure in a vacuum chamber. The gas pressure must be maintained at a low level so that the collision rate of ions is minimized. Anisotropic plasma etching under conditions far from thermodynamic equilibrium is particularly advantageous in the manufacture of ultra-large-scale integrated circuits, as feature dimensions and sidewall profiles can be much more accurately controlled than would be possible using wet etching. This enables the production of integrated circuit features having sidewalls with a precisely defined location that extend substantially vertically from the edges of the masking layer. This is a critical consideration as the ratio of etch depths to feature size or spacing has increased from considerably less than 1, to 1 or more.
Plasma-enhanced chemical vapor deposition (PECVD) has been developed especially by the electronic industry to deposit various types of coatings on a variety of substrates. The process utilizes the energy of plasma to deposit thin films on substrates at low-temperatures. The plasma, or glow discharge that characterizes the process, is generated in a vacuum chamber. There are two basic PECVD processes: a DC glow discharge process and an RF glow discharge process.
The DC glow discharge is generated by applying an electric potential between two electrodes placed within the reactor under vacuum. In the DC glow discharge process, the negative and positive potentials are generally applied to the substrate and chamber wall, respectively. The substrate is generally heated by the bombardment of ions, thereby preventing independent control of temperature of the substrate.
The RF glow discharge, on the other hand, is generated by applying a radio frequency to one of the electrodes while grounding the other. The electrodes may be placed inside the reaction chamber, or they may also be located outside the reaction chamber provided the chamber is made of a non-conductive material, such as glass, quartz, or the like. Because of the difficulty in generating a stable plasma by RF, most of the commercial reactors use parallel electrodes, which are placed inside the reaction chamber and are designed to coat planar substrates. The substrates to be coated are generally placed on the grounded electrode, which can be heated independent of the RF field. Furthermore, a DC bias can be applied to the substrates to control the reaction mechanism. The parallel plates in the RF plasma reactor are generally placed 2-3 cm apart, making such a reactor unsuitable for uniformly coating 3-dimensional parts.
A major problem encountered in the use of plasma reactor equipment, whether it be etching or deposition equipment is the gradual erosion of metal reactor components which are repeatedly exposed to the plasma during the deposition or etching operations. Many of the internal components are fabricated from aluminum or alloys thereof. Such components may include electrodes, shower heads, grids, focus rings, dispersion plates, gas injectors, shields, clamp rings, wafer lift pins, wafer centering rings, alignment rails, paddles, doors, hangers, hinges, holders, gas diffusers, chucks, screws, nuts, bolts, as well as the plasma, etch and diffusion chambers.
Many U.S. patents describe plasma etch and plasma deposition apparatuses. For example, U.S. Pat. No. 6,013,338 to Takashi Inushima, et al. describes a photo-enhanced enhanced CVD apparatus useful for depositing silicon dioxide films of uniform thickness. Another example is U.S. Pat. No. 5,985,098 to Vladimir E. Leibovich, et al., which describes a plasma reactor apparatus having an improved gas delivery mechanism and a thermally-insulated wafer chuck. Still another example is U.S. Pat. No. 6,190,496 B1 to Stephen P. DeOrnellas, et al., which discloses a plasma etch reactor having rare earth magnets for improved plasma confinement. U.S. Pat. No. 6,291,358 B1 to Sujit Sharan, et al. describes a method of operating a PECVD reactor having a chamber wall, a susceptor, a gas inlet, a showerhead positioned over the susceptor, and a power source for providing RF energy. U.S. Pat. No. 6,143,129 to Stephen E. Savas, et al. discloses a plasma etch reactor having an induction coil surrounding the reactor chamber to which RF power is applied, a split Faraday shield interposed between the induction coil and the reactor chamber, and a separate powered electrode for accelerating ions toward a wafer surface. All of the aforecited U.S. patents describe components internal to the plasma reactor chamber which, if made of anodized aluminum, are subject to erosion to the point where they must be replaced after a given period of use. For the purpose of identifying components within the chambers of both plasma CVD and plasma etch reactors, the cited patents are incorporated herein by reference.
The component erosion problem relegates aluminum components, which are exposed to plasma within the reactor chamber, to the category of expendables. Replacement or repair of the eroded items adds to equipment costs and equipment downtime, both of which translate into increased manufacturing costs.
What is needed is a method for protecting the internal components of plasma etch and deposition chambers from the corrosive effects of the plasma generated therein.